Abstract:
Rock drilling is essential in the mining industry. Complexities involved in the drilling process encompassing not only rock properties but also the nature of the drilling action impact the drilling performance and operational costs. Brittleness is a fundamental rock property relevant to rock drilling and excavation works. However, rock brittleness is a concept yet to be investigated. In this study, a new brittleness index developed upon fracture energy quantities withdrawn from the complete stress-strain characteristics in uniaxial compression of rock is presented. A vast independent data on the drilling performance reported elsewhere in the literature was evaluated against the new brittleness index. The results show that the proposed brittleness index successfully describes the performance of different drilling methods including PDC (Polycrystalline Diamond Compact) rotary drilling, roller-cone rotary drilling and percussive drilling.
Introduction
Drilling performance is one of the most important parameters to take into account when evaluating project feasibility and economy in the mining and mineral exploration industry. In this sense, several attempts have been made to assess drilling performance by correlating different rock mechanical and physical properties with the drilling performance including rock texture, grain size, density, P-wave velocity, Unconfined Compressive Strength (UCS), Mohs hardness and rock mass structural parameters (Altindag, 2003; Altindag, 2009; Hoseinie et al., 2008; Taheri et al., 2016). However, a generalised method to relate drilling performance with rock strength characteristics has not been developed yet. This is due to the complexity of interactions among the variables involved in the drilling process encompassing not only rock properties, but also the nature of drilling. In this view, by coupling relevant drilling parameters with relevant rock properties, a reliable drilling performance prediction method can be developed.
On one hand, to predict rock drilling performance and optimisation of drilling operation, tool-rock interaction laws, i.e. the relations between forces acting on the tool in contact with rock, are essential (Detournay and Defourny, 1992; Detournay et al., 2008; Franca, 2010, 2011; Franca et al., 2015; Hustrulid and Fairhurst, 1971a, 1972a; Hustrulid and Fairhurst, 1971b, 1972b). On the other hand, there is not a unique criterion able to describe rock brittleness quantitatively nor consensus about the most suitable and reliable brittleness index to apply to different rock engineering works encountered in the field. For instance, previously a number of different criteria to assess rock brittleness developed upon prepeak stress-strain characteristics in uniaxial compression (Hucka and Das, 1974; Kidybinski, 1981) and upon rock compressive strength, UCS, and tensile strength, TS, (Altindag, 2002; Hucka and Das, 1974; Kahraman, 2002), are not able describe a scale of brittleness to ductility of rock at all (Munoz et al., 2016a; Tarasov and Potvin, 2013; Tarasov and Randolph, 2011).
